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ACUS11 KWNS 211248
SPC MCD 211247

Mesoscale Discussion 1107
NWS Storm Prediction Center Norman OK
0747 AM CDT Wed Jun 21 2017

Areas affected...Portions of the central Gulf Coast

Concerning...Tornado Watch 358...

Valid 211247Z - 211445Z

The severe weather threat for Tornado Watch 358 continues.

SUMMARY...The threat for a few tornadoes near the coast continues
this morning. Additionally, new watch issuance may be required prior
to the 15Z (10AM CDT) expiration of Watch 358.

DISCUSSION...Although the center of Tropical Storm Cindy is
progressing farther away from the ongoing Tornado Watch, conditions
remain modestly favorable for a few brief tornadoes this morning.
Very slow northward movement of a warm front overnight has brought
weak, but adequate surface-based buoyancy to parts of the central
Gulf Coast. Combined with enhanced storm-relative helicity (noted
most clearly in recent KMOB VWP data and the 12Z LIX sounding),
low-level mesocyclones will likely persist in semi-discrete/cluster
modes within confluent bands approaching the coast. Indeed, KEVX
data likely detected a tornado near Fort Walton Beach, FL via a
dual-pol debris signature around 1120Z (620AM EDT).

Persistent moist south/southeasterly flow and pockets of weak
diurnal heating will lead to further inland advancement of
sufficient surface-based buoyancy this morning. However, the
low-level jet peripheral to Cindy will evolve westward through the
day, likely shifting the highest tornado threat closer to the
Mississippi River. While mid-level drying over this part of the
watch has kept convection shallower and more sparse in coverage so
far, the westward evolution of the low-level jet (and related warm
advection) today will likely combine with further destabilization to
foster renewed convection along one or more confluence bands from
Alabama to Louisiana. Recent visible satellite/lightning data
suggest the initial stages of this evolution may be underway across
the central Gulf. Considering the aforementioned environmental
parameters, storms approaching the coast later this morning may
still yield an increased tornado threat. Therefore, a new watch may
be coordinated within the next two hours.

..Picca.. 06/21/2017

...Please see for graphic product...


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